Research is commonly performed on experimental animals that are housed in cages. Typically, these experimental animals are small mammals, such as mice or rats. The research may involve, for example, a drug test, a nutritional test, a genetic test, a test of a surgical procedure, an optogenetics test, or another observation of a physiological or behavioral response to a change in environmental condition or other stimulus. The experimental animals may be divided into a control group and one or more experimental groups. The cages in which the animals are housed may be arrayed, such as in racks.
The housed animals are typically checked in at least two ways: husbandry checks and experimental checks. Husbandry refers to serving the physiological needs of the animals. Husbandry may include observing the wellbeing of the animals, such as, for example, a health check once or twice a day to make sure that none of the animals has developed any symptoms of disease or has died. Health checks may involve looking at the animals through the transparent cage walls in situ without moving the cages, or alternatively pulling the cages partially or completely out of their racks to visually inspect the animals. Experimental checks, meanwhile, are performed to obtain data for the research being conducted. Experimental checks may involve closer examination of the animals than husbandry checks, such as involving opening the cages and removing the animals from the cages. Experimental checks may involve, for example, looking for clinical symptoms in the animals. Experimental checks may also include behavioral tests, such as, for example, water maze or hole board tests, extractions of blood or tissue from the animals, or measurements, such as imaging of the animals.
However, physically contacting the animals, such as through opening the animals' cages, removing them from their cages, and performing measurements on them—or even just approaching the cage to view the animal through the bidirectionally transparent wall, or partially sliding the cage containing the animal out of a rack—can physiologically or psychologically perturb the animals. The consequences of these types of perturbations are often not well understood. Furthermore, there may be inconsistencies in the perturbations, such as differences in when and how the human technicians perform checks across different individual animals. The animals' physiological states and behavior may therefore be altered in ways that are difficult to predict and inconsistent between distinct animals. Thus, these measurement techniques can interfere significantly with the quality of the data obtained from the experiment.
The process of checking the experimental animals may also cause contamination of the animals' living space or the testing equipment. This contamination may, in turn, exacerbate the differences in conditions under which the animals are housed. For example, one human technician may introduce one particular foreign odor into one living space, while another human technician introduces a different odor into another living space. The human technicians who are handling animals from different cages, or using common equipment, may also cause cross-contamination between animals in different cages. In addition, a substantial amount of resources, such as the time and labor of skilled technicians, is expended to monitor the animals. This can account for a significant amount of the total cost of running such an experiment.
Thus, it is desirable to perform checks on experimental animals in a way that yields rich, high-resolution, and reliable data in relation to the number of animals. It is also desirable to avoid physical contact with the animals, inconsistent perturbations of the animals, and cross-contamination between animals in different cages when the animals are checked. Moreover, it is desirable to reduce the amount of time and labor that is expended on running animal experiments.
Thus, it would be desirable to have processes and systems to determine physiological characteristics of experimental animals without or with minimal human technician effort, time, and handling and/or direct observation of experimental animals. It would be desirable for such processes and systems to be efficient, reproducible, and/or relatively inexpensive.
Experimental animals may be monitored, at least in part, by various image capture devices within or outside cages. However, providing image capture devices within cages presents potential issues regarding possible contamination of, decreased lifespan of, and/or increased repair or maintenance such image capture devices. And, providing a set of image capture devices for each cage may be expensive, decreasing the economic efficiency of monitoring experimental animals via image capture devices en masse. Furthermore, certain plastic and other type of cages commonly used to house and monitor experimental animals may include walls that are transparent to visible light, but not transparent to infrared light.
Thus, it would be desirable to have experimental animal cages and monitoring systems that are, at least in part, transparent to infrared light, while at the same time are efficient to use, reproducible, and/or relatively inexpensive.